Ion exchange resins

ABSTRACT

Through the use of a combination of cross-linking agents it is possible to obtain a polymer structure capable of being converted into an ion-exchange resin having improved properties. This combination of cross-linking agents comprises two compounds, one aliphatic and one aromatic, each of which has at least two double bonds.

United States Patent 11 1 3,674,728 Carbonnel et a1. July 4, 1972 [54]ION EXCHANGE RESINS 2,885,371 5/1959 Tavani et al. ..260/2.2

2,891,014 61959 T d t l. 60 2. [72] Inventors: Jack V. Carhonnel; PaulD. Grallnont, 2,891 015 6/1959 2328 2 3 1 both ofchalmyv France; LouisWW1", 3,427I262 2/1969 Corte et al. ....260/2.2 Bruxdles, 3 8 3,544,48812/1970 Corte et al. ..26()/2.2 [73] Assignee: Diamond ShamrockCorporation, Cleve- FOREIGN PATENTS 0R APPLICATIONS land, Ohio 3,8925/1958 Ja an 22 F1led: Apr1l30, 1970 5,740 7/1958 Jagan 21 Appl. No.:33,512 14.012 1961 Japan 5,741 1958 Japan Related US. Application DataPrimary Examiner-Melvin Goldstein 1631 cmt'nuauon'm'pan of Attorney-RoyDavis, C. Thomas Cross, Timothy E. Tinkler. 19681 abandoned John .I.Freer, Neal T. Levin, Leslie G. Nunn, Jr., Helen P.

Brush and John C. Tiernan [30] Foreign Application Prlorlty Data Jan.30, 1967 France ..6792937 [571 ABSTRACT Through the use of a combinationof cross-linking agents it is [52] US. Cl. ..260/2.2 R, 260/2.1 E,260/80.7, o ibl to obtain a polymer structure capable of being con-/80." verted into an ion-exchange resin having improved properties. [51]Int. Cl. ..C08f 15/40 This combination of cross-linking agents comprisestwo com- [58] Field of Search ..260/2.l E, 2.2, 80.78 pounds, onealiphatic and one aromatic, each of which has at least two double bonds.f C'ted [56] Re erences 1 l C m, N Drawings UNITED STATES PATENTS IONEXCHANGE RESINS REFERENCE TO A COPENDING APPLICATION This application isa continuation-in-part of our copending application Ser. No. 698,692,filed Jan. 18, 1968 now abandoned.

BACKGROUND OF THE INVENTION This invention relates in general to themanufacture of ionexchange resins, both anionic and cationic.

It is well known to form an ion-exchange resin using divinylbenzenealone as the cross-linking agent. While these resins have advantageousproperties, including improved resistance to oxidation, certaindifliculties have also been noted. Most importantly, because of therigidity of the bond formed using divinylbenzene as a cross-linkingagent, the ultimate ionexchange resin has shown poor resistance to theexpansion and contraction which occurs during the service cycle of theresin.

It has been proposed, for example in U. S. Patent No. 2,645,621, that amonovinyl aromatic compound be copolymerized with an aliphatic compoundhaving a number of double bonds. Experience has shown, however, that thecationic sulfonated resins obtained from such a copolymer are quitefragile.

In order to produce a cation-exchange resin having carboxylic acidgroupings, a copolymer of acrylonitrile and divinylbenzene has beenproposed. Unfortunately however, it has once again been found that thisresin has little resistance. to breakage when passing from theregenerated to the exhausted form. In order to overcome thisdisadvantage the use of certain vinyl esters has been proposed. Whileimprovements are obtained, the results are still not entirelysatisfactory.

It has also been proposed to provide a completely crosslinked,water-insoluble, ion-exchange resin, especially one containingcarboxylic acid groups, by copolymerim'ng an ester of acrylic acid witha combination of cross-linking agents, both aliphatic and aromatic. Suchresins, however, are expensive and have a poor resistance to osmoticshock.

SUMMARY OF THE INVENTION Therefore it is an object of this invention toovercome the above-mentioned disadvantages and to provide an ionexchangeresin which will pass from the regenerated to the exhausted form withoutundergoing cracking or breaking of the resin itself.

It has now been found that a water-insoluble ion-exchange resin isobtained by attaching anion or cation exchange groups to a polymerskeleton, which polymer skeleton consists of a copolymer of a monomerselected from the group consisting of acrylonitrile, styrene andmethylene glutaronitrile and a combination of two-cross-linking agents,each of which has at least two double bonds, one of said cross-linkingagents being aliphatic while the other is aromatic.

Ion-exchange resins such as described above have elastic properties notpossessed by corresponding ion-exchange resins made from a polymerskeleton containing only one cross-linking agent, e.g., divinylbenzene.The resins of this invention are extremely durable, are resistant toosmotic shock and show relatively little tendency to expand and contractwhen passing from the regenerated to the exhausted form and back. Theseresins also exhibit improved exchange rates. Other characteristics andadvantages of the invention will appear during the description whichfollows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to form the polymerskeleton of the present invention, a monomer selected from the groupconsisting of acrylonitrile, styrene and methylene glutaronitrile iscopolymerized by a conventional suspension copolymerization technique,with a combination of two cross-linking agents, each containing at leasttwo double bonds, one agent being aliphatic and the other aromatic. Thealiphatic crow linking agents useful, which also include thecycloaliphatic cross-linking agents, are: 1,3-butadiene, isoprene;piperylene; chloroprene; 2,3-dimethyl-l,3-butadiene; 2,3-pentadiene;1,4-pentadiene; 1,5-hexadiene, 2,4-hexadiene; 2,5-dimethyl-2,4-hexadiene; octadiene; 3,7-dirnethyl-2,4-octadiene; 2methyl-6-methylene-2,7 octadiene; 1,3-decadiene; 1,3,5-hexatriene;hexachlorocyclopentadiene; cyclopentadiene and dicyclopentadiene.Divinyl and trivinylbenzene are the aromatic cross-linking agents whichare useful.

Following the above polymerization, the polymer skeleton, which, sinceobtained by a suspension polymerization process will be in the form ofbeads, is converted to the desired ionexchange resin. This is done byany of the methods well known to those skilled in the art ofion-exchange resin production and by these known means either an anionicor cationic exchange resin may be obtained. It will be understood that,depending upon the method used to form the ultimate ion-exchange resinand the identity of the monomer chosen, resins which are either strongor weak cation exchangers or strong or weak anion exchangers may beprovided.

It will be apparent to one skilled in the art that the properties of theultimate exchange resin may be varied somewhat by changing the weightratio of aromatic to aliphatic cross-linking agent. Furthermore, thetotal amount of cross-linking agents which are present in combinationwith the monomer may vary over wide limits depending upon the resultsdesired. Thus the amount of cross-linking agents present may vary withinthe range of from 0.1 to 50 percent by weight of the total polymerizablemixture.

In order that those skilled in the art may more completely understandthe invention, the following illustrative examples are afiorded.

EXAMPLE] For the polymerization reaction, into a 500 cc. flask, providedwith a stirrer, cooling means and a thermometer, are placed 220 cc. ofsaturated brine and a commercial dispersion agent. There is then addedwith stirring a mixture containing 79.5 grams of acrylonitrile, 19.5grams of divinylbenzene (DVB, 62 percent by weight), 1 gram of isopreneand 1.2 grams of benzoyl peroxide percent by weight). Polymerization isconducted for 7 hours at a temperature between 55 and 60 C. followingwhich the polymer beads are filtered, washed and dried.

In order to convert the polymer skeleton into a weak-acidcation-exchange resin, 20 grams of the polymer beads are placed in aflask together with 150 cc. of 60% H 80. and refluxed between 137 and140 C. for 7 hours. The resin so obtained has a total capacity of 4.7equivalents per liter in the hydrogen from, 2.68 equivalents per literin the sodium form and 8.3 equivalents per kilogram in the sodium fonn.

EXAMPLE2 Following the procedure of Example 1, a mixture is polymerizedwhich mixture comprises 78.5 grams of acrylonitrile, 19.5 grams of DVB(62 percent), 2 grams of isoprene and 1.2 grams of benzoyl peroxide (85percent). After hydrolysis, also as in Example I, there is obtained acation-exchange resin having a total capacity of 4.41 equivalents perliter in the hydrogen form, 2.88 equivalents per liter in the sodiumform and 7.78 equivalents per kilogram in the sodium form.

EXAMPLE3 Following the procedure of Example I, a mixture of 79.7 gramsof acrylonitrile, 16.3 grams of DVB (61.2 percent, 4 grams of isopreneand 1.2 grams of benzoyl peroxide (85 percent) is polymerized for 7hours at a temperature between 40 and 60 C.

The polymer beads obtained by this process are then con verted to aweak-acid cation exchange resin by hydrolysis of 20 grams of thepolymerized beads in 150 cc. of H 80, (60 percent) under the conditionsdescribed in Example 1. This resin has a total capacity of 4.9equivalents per liter in the hydrogen form, 3.3 equivalents per liter inthe sodium form and 8.06 equivalents per kilogram in the sodium form.

EXAMPLE 4 The procedure of Example 3 is followed exactly with the exception that the acrylonitrile is replaced with a molar equivalentamount, 129 grams, of methyl acrylate. In this instance the weak-acidcation-exchange resin so formed has a total capacity of 4.7 equivalentper liter in the hydrogen form, 2.98 in the sodium form and 7.85equivalent per kilogram in the sodium form. Further, the resin swells 90percent in volume when passing from the PH to the Na+ form, as opposedto only 48.5 percent for the resin of Example 3. Moreover, it is foundthat placing the resin of this example in the H+ form, into a 1Nsolution of NaOH, results in 50 percent of the beads having a sizegreater than 0.5 millimeters, most of the resin being of this size,being broken, evidencing their poor resistance to osmotic shock.Substantially none of the beads of the resin of Example 3 are brokenunder identical conditions.

EXAMPLE 5 Using the apparatus of Example 1, a polymerization suspensionmedium is prepared comprising 250 cc. of water and 1.25 grams ofpoly(vinyl alcohol). There is then added with agitation a mixturecomprising 102 cc. of styrene, 0.15 cc. DVB (61 percent), 1 gram ofisoprene and 1 gram of benzoylperoxide. Polymerization is conducted for8 hours at a temperature between 70 and 85 C. and then for 1 hour at 88C., following which the polymer beads are filtered, washed and finallydried in an oven at 70 C.

These polymer beads are then chloromethylated and subsequently aminatedwith trimethylamine. By this means there is obtained an anion-exchangeresin having a total capacity of 1.2 equivalents per liter in thechloride form and 3.34 equivalents per kilogram in the chloride form.

EXAMPLE 6 Using the apparatus of Example 1 there is added to adispersing medium as in Example 5 a mixture of l 16 grams of styrene,17.7 grams of DVB (61 percent), 1.35 grams of isoprene and 0.3 grambenzoyl peroxide. This mixture is polymerized at 8586 C. for 8 hoursfollowing which it is filtered, washed and dried.

The polymer beads obtained are then sulfonated, using 1 part of polymerbeads to 7 parts, by weight, of H SO (98 percent), over a period of 8hours. The strong-acid cationexchange resin obtained by this means has atotal capacity of 2.02 equivalents per liter in the sodium form and 4.72equivalents per kilogram in the sodium fonn.

EXAMPLE 7 Following the procedure of Example 6, a mixture comprising 112grams of styrene, 17.7 grams DVB (61 percent), 5.4 grams of isoprene and0.4 gram benzoyl peroxide is polymerized. The polymer beads so obtainedare sulfonated, also by the procedure described in Example 6, and arefound to have a total capacity of 1.77 equivalents per liter in thesodium form and 4.44 equivalents per kilogram in the sodium form.

EXAMPLE 8 Following the procedure of Example 1, a mixture of 80.5 gramof acrylonitrile, 19.5 DVB (62 percent) and 1.2 grams of benzoylperoxide (82 percent) is polymerized. Upon hydrolysis the polymer beadsare found to have a total capacity of 4.59 equivalents per liter inhydrogen form, 2.51 equivalents per liter in the sodium form and 8.76equivalents per kilogram in the sodium form. It is found that theseion-exchange resin beads in the hydrogen form, i.e., the regeneratedform, break when placed in contact with a l N solution of NaOH. Thisexample therefore illustrates the advantage of using a combination ofcross-linking agents in the polymerization process. EX- AMPLE 9Operating as in Example 1 but at a temperature of 40-60 C. for a periodof 7 hours, a mixture comprising 83.7 grams of acrylonitrile, 16.3 gramsof DVB (61.2 percent) and L2 grams benzoyl peroxide (82 percent) ispolymerized. Following hydrolysis these ion-exchange resin beads arefound to have a total capacity of 3.43 equivalents per liter in thehydrogen form, 1.08 equivalents per liter in the sodium form and 8.7equivalents per kilogram in the sodium form. As in Example 8, however,it is found that when these beads, in the hydrogen form, are placed incontact with a NaOH solution, they break.

EXAMPLE 10 To illustrate the use of isoprene alone as the cross-linkingagent, the procedure of Example 1 is followed using a mixture comprising98 grams of acrylonitrile, 2 grams of isoprene and 2.8 grams of benzoylperoxide (85 percent). The resultant polymer beads are hydrolyzed inorder to produce a weak-acid cation-exchange resin having a totalcapacity of 1.32 equivalents per liter in the hydrogen form, 0.196equivalent per liter in the sodium form and 10.5 equivalents perkilogram in the sodium form. While these resin beads in the hydrogenfonn do not break when contacted with a NaOH solution, it is found thatthey are extremely fragile and moreover that they swell enormouslyduring the service cycle. When placed under a microscope the resin beadsare noted to be spongy in appearance with approximately 14 percent ofthe beads being completely hollow. Beads prepared using a combination ofaromatic and aliphatic cross-linking agents do not have this appearancenor does excessive swelling occur when operating under the sameconditions.

EXAMPLE ll As a further example of the use of only an aliphaticcrosslinking agent, a mixture of 96 grams acrylonitrile, 4 grams ofisoprene and 2.8 grams of benzoyl peroxide 85 percent) is polymerizedaccording to the process of Example 1. After hydrolysis thecation-exchange resin formed is found to have a total capacity of 2.45equivalents per liter in the hydrogen form, 0.7 equivalent per liter inthe sodium form and 10.2 equivalents per kilogram in the sodium form.Once again, while the resin beads do not break in contact with the NaOHsolution, they are found to be quite fragile and to swell excessively.

EXAMPLE 12 Using the dispersing medium of Example 6 and the apparatus ofExample 1, a mixture of 92 grams of styrene, 8 grams of isoprene and 2.5grams of benzoyl peroxide is polymerized at a temperature of 85 to 86 C.for 15 hours.

The resin beads so obtained, after washing and drying, are placed incontact with a 95 percent solution of H,SO However, when it is attemptedto sulfonate these beads at a temperature of C., it is found that theydissolve.

EXAMPLE 13 In order to illustrate the use of an aliphatic cross-linkingagent other than isoprene, the following mixture is polymerizedaccording to the process of Example I; 87.7 grams of acrylonitrile, 6.5grams of DVB (61.2 percent), 5.8 grams of cyclopentadiene and 1.2 gramsof benzoyl peroxide 85 percent). Upon hydrolysis a weak-acidcation-exchange resin is obtained which has a capacity of 1.98equivalents per liter in the hydrogen form, 0.74 equivalent per liter inthe sodium form and 9.13 equivalents per kilogram in the sodium form.When these resin beads in the hydrogen form are placed in contact with 1N solution of NaOH they do not break.

EXAMPLE l4 In contrast to Example 13, a mixture containing 94.2 gramsobtained as described in this example exhibits 6 percent attrition. Bycomparison, the anion-exchange resin obtained according to the practiceof the present invention in Example 5, shows an attrition of only l2percent.

The following table clearly illustrates the advantages ob- TABLE 6 aWeight percent of total polymerizable ingredients. b During servicecycle.

When pass 1925 9. 29-

of acrylonitrile, 5.8 grams of cyclopentadiene and 1.2 grams of benzoylperoxide is polymerized. When an attempt is made to convert the polymerbeads to a weak-acid cation-exchange resin by hydrolysis in a 60 percentsolution of H 50 however, it is found that the polymer beads, which wereoriginally quite deformed, dissolve.

EXAMPLE Using the dispersing medium and polymerization conditions ofExample 5, 102 cc. of styrene, 0.753 gram of DVB (61.2 percent), 2.84grams of hexachloropentadiene and 1 gram of benzoyl peroxide arepolymerized to form the desired polymer skeleton. As in Example 5 thepolymer beads are chloromethylated followed by amination withtrimethylamine to form a strong-base anion-exchange resin having acapacity of 1.4 equivalents per liter in the chloride form and 3.84equivalents per kilogram in the chloride form.

Using the attrition test described more completely in U.S. Pat. No.3,418,262, which test comprises subjecting resin beads to mechanicalwear under specified conditions for a certain period of time followed bymeasuring the amount of beads that are broken at the end of this test,it is found that the resin ing item the regenerated to the exhaustedform.

tained by the practice of the present invention through reference tocertain of the preceding examples.

Although the invention has been described with reference to certainspecific embodiments thereof, it is not to be so limited since changesand alterations may be made therein which are within the full andintended scope of the invention, as defined in the appended claims.

We claim:

1. The weak-acid, cation-exchange resin obtained by hydrolysis of acopolymer of:

a. acrylonitrile;

b. an aromatic cross-linking agent selected from the group consisting ofdivinylbenzene and trivinylbenzene and, an aliphatic cross-linking agentselected from the group consisting of 1,3-butadiene; isoprene;piperylene; chloroprene; 2,3-dimethyl-l,3-butadiene; 2,3-pentadiene;1,4-pentadiene; 2,4-hexadiene; 2,5-dimethyl- 2,4-hexadiene; octadiene;3,7-dimethyl-2,4-octadiene; 2- methyL-methylene-Z,7-octadiene;l,3-decadiene; 1,3,5- hexatriene; hexachlorocyclopentadiene;cyclopentadiene and dicyclopentadiene.

UNITED STATES PATENT AND TRADEMARK ()FFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,674, 728

Q DATED July 4, 1972 ANVENTORG) Jack Carbonnel etal.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 6, line 45 delete octadiene; "1 first occurrence Signed andScaled this Sixteenth D3) 0f 0mm I979 iSEAL] Attest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Ojficer Acting Commissionerof Patents and Trademarks

